Need help with odd quench result

samuraistuart

samuraistuart

Joined
Dec 21, 2006
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3,158
Hey guys, I had a frustrating experience just now. I am making a chef's knife for a client out of Aldo's Blue 2. I've used it before, always normalized and cycled even tho I'm only doing stock removal. For knives that size, I always grind pre HT. However, I left MORE meat on the edge than normal this go around. ~0.050" and a spine width of 0.135". It's a hefty blade that "would" get thinned down a LOT post HT, obviously.

This time I decided to skip the normalizing/cycling and simply austenitize/soak/quench. Parks 50 oil at 90°. 1490°f aus temp. The usual stuff.

Out of the quench, the ENTIRE blade "bacon warped". I can't say that I've EVER had an entire blade bacon warp. I've had an edge bacon warp because I had ground it too thin pre HT. That wasn't the case this go around at 0.050", plus the fact that the spine warped just as well. Quench was tip down, straight into oil. I've quenched edge first, tip down, never finding any issue one way or another.

I'm just left scratching my head as to WHAT happened, hoping I can scoot around it next go around. I have enough Blue2 for one more chef's knife, and don't want anything to go wrong with it. The 2nd attempt will be normalized for SURE, like I always had done with that Blue2, especially now that I'm wondering if there is some weird stress/tension in that particular sheet.

Any thoughts?
 
what is Aldo's Blue 2? is that a homogenous steel?
is the oil old?
did the blade Harden?

can you heat treat again to anneal and straighten this warped one?
and then try the quench again
 
I haven’t tried any of it without normalizing and cycling, so I can’t help you there.

Warren
 
I have some warp from time to time, but not any bacon edge. I always normalize, so I don't know if that was where you erred, but suspect it is the culprit.
 
To help prevent this, shorten the pre-grind.

Steels grow upon hardening, shallow hardening steels sometimes will not fully harden from edge to spine. Also, if it is fully hardened and if the spine is longer than the edge, the spine can grow longer than the edge causing the bacon effect. Look to see if the spine is rounded and the tip is dropped from before HT.

Hoss
 
Thanks to everyone for replying. That is what I am guessing as well. Should have normalized it. But that "shouldn't" be the issue. It "may" be the issue, but it "shouldn't" be. I'll leave that there without saying more. How many times has the entire blade bacon warped on you? I'm guessing never.

Harbeer: Yes, Aldo had at one time homogeneous Blue 2 in .135" sheets. The oil is not old at all, still as clear/clean as the day I received it (I clean the ATP flakes often as well). Yes, the blade is extremely hard, as would be expected. No problems hardening at all. Just the distortion issue. After taking a better look at the blade (once I cooled off myself), it may be salvageable with a little magic in the temper oven as well.

Shane, full flat grinds, and very very even and flat on both bevels. I like to draw file once bevels are shaped, just to ensure it's pretty flat.

Hoss, I took a look at it just now. Spine is not rounded, it is still very square (assuming you mean the shoulders of the spine), and the tip did not drop (understand negative sori upon oil quench shallow hardening steels). The only change in the blade made was, as you look down at the spine (or up at the edge), there is an "S" bend. Maybe not as bad as "bacon", but 2 definite bends to form an "S". Like I mentioned, this may be fixable. I'll be doing that this PM.

Thanks again, guys. I'm marking in my notebook for the next Blue 2 project with the last bit of that steel I have, "NORMALIZE A MUST!!!"
 
Stuart,
The steel you have is a great high hardness steel. It is also fairly shallow hardening. That is one of the reasons to use Hitachi white and blue steel. When hardening in a fast oil or water, the edge will harden quickly. The thicker spine may harden less, or not at all. This is how we create a hamon. These steels can even auto-hamon.

Here is how the metallurgy works out:
1) The thin and low mass edge drops to 900°F very rapidly - the edge steel stays austenite as it passes the pearlite nose.
2) The thicker portions with more mass may not drop fast enough to fully pass the pearlite nose - the spine steel becomes a mix of pearlite and austenite.
3) As the edge reaches 400°F, it starts to convert to martensite. While this conversion may take time to be complete by 200°F, the actual conversion at the atomic level happens at the speed of sound. When a cube of atoms switches from FCC to BCC it is instantaneous and very hard. The cube also gets bigger.
4) The thicker spine cools to 400° slower and is still a pearlite/austenite mix as the edge converts to hard martensite. Depending on the amount of austenite in the mix, the spine can range from soft to medium hard as any austenite starts to convert.
5) The martensite expands upon conversion and increases the edge length. If the spine is still soft enough, it will expand the edge and compress the spine, causing the curvature called sori.
6) If the thicker spine is also converting to a harder structure of pearlite and martensite, it will resist the pressure to compress. This will cause the edge to move sideway to find an outlet for the growth in length. Sometimes it moves in one direction, creating a warp. The expansion may be both left and right .... creating a bacon edge. How hard the spine is as it approaches the tip can make that tip area less bacony, but the whole edge may bacon in some cases.

Normalizing can make smaller grains and prepare the structure for the fastest conversion rate upon the final quench, thus allowing the spine to convert closer to the timing of the edge. If they are more or less in the same time frame, the blade stays straight. The other factor that enters in this is the austenitizing temperature. Lower temps can decrease bacon edge.
 
Thanks for taking the time to write that up, Stacy. I understand the dynamics of shallow hardening steels and sori/water and negative sori/oil and why that happens. The Blue 2 blades I've made in the past have all had auto hamons, close the spine. I've never heard of a blade taking an "S" bend, or "bacon", due to those same dynamics, but I've got a LOT to learn about this stuff. I've used W2 before as well on chef's knives, but honestly, because they were Aldo's W2 bar stock, they were normalized and cycled prior to hardening. I've just never had a shallow (or deep) hardening steel distort this much in a quench before. (besides the cases where my edge was too thin, and even then the spine didn't bend, only the edge)
 
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